Pacing Cycle Length-Dependent Electrophysiological Changes in Left Atrium: Poor Validity of Using Low Voltage Area and Slow Conduction Area under Specific Pacing Cycle Length as Absolute Substrates of Atrial Fibrillation.

Background: Pacing cycle length (PCL)-dependent changes in left atrial (LA) electrophysiological properties have not been fully elucidated.

Objective: To elucidate these changes using a high-resolution mapping system.

Methods: Forty-eight patients underwent atrial fibrillation ablation with RHYTHMIA HDx™. Paired LA maps under a baseline PCL (600 ms) and rapid PCL (300 ms) were acquired after pulmonary vein isolation under right atrial appendage pacing. The PCL-dependent change in the low-voltage area (LVA) (area with <0.5 mV bipolar voltage), LA activation time (interval from first LA activation to wavefront collision at lateral wall), regional mean voltage, regional mean wave propagation velocity, and slow conduction area (area with <0.3-m/s wave propagation velocity) were quantitatively analyzed.

Results: Under the rapid PCL, the total LVA was significantly increased (7.6 ± 9.5 vs. 6.7 ± 7.6 cm², p = 0.031), especially in patients with a ≥10 cm² LVA on the baseline PCL map (21.5 ± 9.1 vs. 18.1 ± 6.5 cm², p = 0.013). The LA activation time was also prolonged (87.9 ± 16.2 vs. 84.0 ± 14.0 ms, p < 0.0001). Although the rapid PCL did not decrease the regional mean voltage, it significantly decreased the regional mean wave propagation velocity and increased the slow conduction area in all measured regions.

Conclusion: LVA and slow conduction area can be emphasized by rapid PCL LA mapping. There may be poor validity in using these areas as absolute atrial fibrillation substrates without considering the PCL-dependent changes.